1. Field of the Invention
The present invention relates to an inverse rectifier for use with a high voltage transformer in an x-ray generator, and in particular to such a rectifier having two switching transistors which alternately connect a load output to be positive and negative poles of a constant voltage source.
2. Description of the Prior Art
An inverse rectifier having two switching transistors which alternately connect a load output to either the positive pole or the negative pole of a constant voltage source is described in German No. OS 27 50 455. This inverse rectifier forms a component of an x-ray diagnostic generator which, as a consequence of the supply of the high voltage generator with medium frequency, can be made smaller and lighter in weight than would be the case with a comparable transformer fed with mains frequency. Due to the winding and cable capacitance transformed at the primary side, the high voltage transformer represents a capacitive load. A parallel resonant circuit can thus be formed for a fixed drive frequency by means of an inductance which matches this capacitive load. In the equivalent circuit, the inverse rectifier accordingly controls a parallel resonant circuit with its resonant frequency and with variable pulse duty factor. The resonant circuit energy, and thus the amplitude of oscillations, are varied by changing the pulse duty factor.
In an inverse rectifier of the type described above, two critical operating conditions must be considered for which the load represents a short-circuit for the inverse rectifier. These critical operating conditions are (1) cut-in moment, and (2) short circuit of the high voltage due, for example, to flashover in the x-ray tube.